Transceiving data over an infrared transmission path between two devices is known. For example, infrared is used to transceive data between a remote controller and a television, a radio, an audio-amplifier, a video cassette recorder, etc.
To transceive data over an infrared ("IR") path between two devices, each device needs to be equipped with an IR receiving circuit and an IR transmission circuit. The IR receiving circuit includes a light receiving diode that receives data via the IR path. The IR receiving circuit further includes an amplifier section and a data detection circuit which are designed to accommodate a large dynamic range input signal. For example, the magnitude of the input data may vary greatly from 10 mAmps (when the devices are relatively close, i.e., less than 10 centimeters apart) to 100 nAmps (when the devices are relatively far apart, i.e., greater than 1 meter apart).
The IR transmission circuit includes a light transmitting diode which transmits data over the IR path. The light transmitting diode is pulsed on and off at a given frequency (2 microsecond pulses for amplitude shift keying, 125 nanosecond pulses for four pulse position modulation). The power level at which the diode is pulsed is at a fixed level such that when it is on, it is drawing at least 10 mAmps.
When both the IR receiving circuits and IR transmission circuit are included in the same device, the IR receiving circuit "picks up" the IR signals being transmitted by the IR transmission circuit. This is sometimes referred to as cross-talk. When the IR receiving circuit and IR transmission circuit are on the same IC, the cross-talk is even more pronounced. Cross-talk, however, is controlled by employing echo cancellation circuitry. In essence, echo-cancellation circuitry rejects the data received by the IR receiving circuit when the IR transmitting circuit is transmitting. While echo-cancellation eliminates most of the effects of cross-talk, it does not eliminate them all. For example, the magnitude of the cross-talk signal received by the IR receiving circuit may be considerably greater than an actual data signal. When this occurs, the IR receiving circuit is biased to receive a larger magnitude data signal than may actually be received from the other device, thereby causing the IR receiving circuit to miss low magnitude data signals. Similar missed data signals occur for other wireless transceiving circuits.
Therefore, a need exists for a method and apparatus that fuither reduces the effects of cross-talk in wireless transceiving circuits.